[The_K_Man]

I found this tire pressure/temperature gradient chart online, and am curious as to what it is suggesting. Across the top are, in intervals of 2psi, a range of typical recommended cold tire pressures for cars and light trucks. Down the side column are, in intervals of F°10, ambient outdoor temperatures.

My 2010 Honda's Tire and Load decal, on the drivers B-pillar, specifies 32psi cold pressure for all four tires.

Now, the chart seems to use F°70 as its baseline for 'cold'(not driven for at least three hours, or earliest part of day) tire pressures. So in my example, if the early morning ambient temperature is 70° or higher, I can maintain the 32psi recommended by Honda in my Accords tires.

However, if the ambient temperature is 60° but below 70°, the chart recommends adding 1psi, or keeping my tires at 33psi. 50-59°: 34psi, and so on. By late January, with morning temperatures in the teens or low twenties fahrenheit, the chart suggests I keep 37-38psi cold pressure in my tires!

What is this tire website's rationale behind inflating my tires to 1psi higher cold pressure per 10° below 70°, and should I do so?

Historically, if I set my cold tire pressures to 32psi in summer, with a morning temperature of 65-75°F, and then checked them in the fall, when it was only 45°, I would inflate them back up to the 32psi listed on my Tire and Load sticker on the door frame. In other words, I'd maintain 32-33psi cold pressure in my Accord's tires year-round, be it the blazes of July, or the icy pits of January or February.

So which procedure - mine, or the chart's - is correct?

 

[Hudouc]

I do exactly what you do as well. The chart seems incorrect.

 

[jackpine]

I do what you do also. I suspect the rationale behind increasing the cold tire pressure when temperatures drop is to achieve nearly the same "warm" (running) pressure on the road in cold temperatures as you would have when it's hot outside. I can certainly see that if the road is below freezing, your tires would never heat up to the same level as they would be on a 100 degree day, and you would be driving on tires that were inflated to a lower value.

I don't know that this difference is important, but I don't think you would hurt anything by following the guidance in the chart.

- Jack

 

[andrewtl96]

Historically, if I set my cold tire pressures to 32psi in summer, with a morning temperature of 65-75°F, and then checked them in the fall, when it was only 45°, I would inflate them back up to the 32psi listed on my Tire and Load sticker on the door frame. In other words, I'd maintain 32-33psi cold pressure in my Accord's tires year-round, be it the blazes of July, or the icy pits of January or February.

This is exactly what I do. No need to really overcomplicate it honestly.

 

[highvoltage]

Fill or check your tires to make sure they are at proper pressure for the ambient temperature in your area for that day. Then drive; minor variations in temperature during your driving period will not adversely affect pressure. It takes a 10° change in temperature to make a 1 psi change in pressure, which is pretty close to what the chart says. But constantly chasing chart temperatures is unnecessary.

 

[The_K_Man]

Fill or check your tires to make sure they are at proper pressure for the
ambient temperature in your area for that day. Then drive; minor variations
in temperature during your driving period will not adversely affect pressure.
It takes a 10° change in temperature to make a 1 psi change in pressure,
which is pretty close to what the chart says. But constantly chasing chart
temperatures is unnecessary.

Thanks everyone for your inputs on this subject!

1) I do understand what the chart is suggesting, and the dynamics of changes in ambient temperature involved in its formulation. If anyone wants to weigh in on the concept of "Is 32psi at 80°F the same as 32psi at 30°?" that would be appreciated, since we all know that air becomes less dense at higher temperatures.

2) I have done, sort of, what the chart recommends, just not as much of a change. When I showed the chart to a retired engineer who is a customer where I work, he said, "Thirty seven psi when it's 30 degrees? That'll really F- up your tires!" LOL.

Seriously though, from December through March, I run my cold inflation pressures a little higher, 34psi for instance. I find I get a little more bite on slush and snow, especially with these wide low profile 50-series tires that the 2010 Accord EX and EXL came with.

3) Highvoltage: "chasing the chart" isn't even an issue. Even if one did maintain the tire inflation schedule suggested in it, that would require no more than ten to twelve adjustments per year for tire pressure maintenance - about as often as is recommended by everyone from AAA to 'Z Z's Automotive' down the block.

 

[emeron]

I swap to winter tir

Thanks everyone for your inputs on this subject!

1) I do understand what the chart is suggesting, and the dynamics of changes in ambient temperature involved in its formulation. If anyone wants to weigh in on the concept of "Is 32psi at 80°F the same as 32psi at 30°?" that would be appreciated, since we all know that air becomes less dense at higher temperatures.

To achieve 32psi at 80⁰F you will need fewer gas molecules than what you would need to get 32psi at 30⁰F because gas molecules get excited and exert more forces to the inside wall of the container (tire). Which is the same thing as saying you will need more airs at 30⁰F to read 32psi than the amount of 80⁰F airs to get 32psi.

The ability of gas molecules that make up regular air to create pressure drops about 1psi every 10⁰F. This statement has been verified by actual measurements by others in pressure and temperature ranges relevant to driving, and found about correct with 10% error margin.

Some people (not me) use nitrogen in tires because its pressure fluctuation is smaller than air. Some other people use nitrogen in tires because it sounds cool.

 

[The_K_Man]

To achieve 32psi at 80⁰F you will need fewer gas molecules than
what you would need to get 32psi at 30⁰F because gas molecules
get excited and exert more forces to the inside wall of the container
(tire). Which is the same thing as saying you will need more airs at
30⁰F to read 32psi than the amount of 80⁰F airs to get 32psi.

Got all that.

Now, for the purposes of this discussion, I will use two abbreviations:

'PSIa' = PSI actual

'PSIi' = PSI indicated (via pressure gauge, etc)

What I want to know is, if, at 70°F, as on that chart, 32PSIa and 32PSIi were within 1PSI of each other, allowing for gauge error, what PSIi, at 30°F, would the tire have to be inflated to, in order for there to be 32PSIa in that tire?

Would it be as much as indicated in that chart for that given pressure(32psi), or less or more?

 

[qman]

1) I do understand what the chart is suggesting

Please explain it to me. I think the chart is telling me that if my OEM Recommended Tire Pressure is 32 psi then I should put in 39 psi if it's 0 degrees out. That makes absolutely zero sense.

If it's 0 degrees out I put in 32 psi. If it's 70 degrees out I put in 32 psi. I can only guess that it is trying to say 32 psi at 0 degrees will expand to 39 at 70 degrees. If that's what it is trying to say then it is not clear at all.

 

[The_K_Man]

Please explain it to me. I think the chart is telling me that if my
OEM Recommended Tire Pressure is 32 psi then I should put
in 39 psi if it's 0 degrees out. That makes absolutely zero
sense.

If it's 0 degrees out I put in 32 psi. If it's 70 degrees out I put in
32 psi. I can only guess that it is trying to say 32 psi at 0 degrees
will expand to 39 at 70 degrees. If that's what it is trying to say
then it is not clear at all.

Perhaps it is temperature compensated readings.

In other words, a gauge reading of 39psi at 30°F is compensating for a gauge reading of 32psi at 70°.

There are ‘temperature compensated’ tire gauges that perform this function for you. For the majority of folks with ordinary tire gauges, there’s the chart.

That is what I think the chart is saying, even though the webpage publishing it doesn't explicitly state so.

I do compensate some during winter, but again not as much as the chart recommends. If I inflate my tires to as much as 3psi cold, on my gauge, over what Honda recommends for my Accord, it rides like a pulpwood wagon. The ride is already firm enough at 33-34psi cold indicated, and like my customer friend said, 37-39psi cold sounds “ridiculous” for a passenger sedan, let alone his minivan, during any season.

My two go-to gauges are both less than 1psi off from the ones at my local mechanic’s.

 

[emeron]

Got all that.

Now, for the purposes of this discussion, I will use two abbreviations:

'PSIa' = PSI actual

'PSIi' = PSI indicated (via pressure gauge, etc)

What I want to know is, if, at 70°F, as on that chart, 32PSIa and 32PSIi were within 1PSI of each other, allowing for gauge error, what PSIi, at 30°F, would the tire have to be inflated to, in order for there to be 32PSIa in that tire?

Would it be as much as indicated in that chart for that given pressure(32psi), or less or more?

Pressure is not an absolute measure of something for example mass. Pressure is a derivative quantity. For gasses, it is a function of:
1. How many molecules
2. Volume of the container that's containing the movement of the molecules
3. Temperature

There is something called indicated pressure vs. absolute pressure, but that's about the atmospheric pressure. Meaning when you measure the pressure of a gas in a container, and get a positive reading, the absolute pressure there is actually the reading on the dial plus the pressure of the air column above. If your tire measures 30psi at sea level, it will give a reading of 44.696 in space, assuming both readings were taken at the same temperature.

The only thing that's absolute about the air in a tire is the number of gas molecules that make it up. Assuming no leaks.

When the temperature increases, the gas molecules get angrier, and hit the walls harder. Which affects higher pressure.

Having said that, I also want to stick a needle to the auto manufacturers. "Cold temperature" what is it? Living in Canada that's 40 degrees on a pleasant day. Living in Cairo it is 100 degrees on a pleasant day.

What is really relevant to tire pressure specs is;
1: What do you mr carmaker consider as operating temperature of the tire
2: What pressure do you need this tire at operating temperature

 

[The_K_Man]

Pressure is not an absolute measure of something for example mass. Pressure
is a derivative quantity. For gasses, it is a function of:
1. How many molecules
2. Volume of the container that's containing the movement of the molecules
3. Temperature

There is something called indicated pressure vs. absolute pressure, but that's
about the atmospheric pressure. Meaning when you measure the pressure of
a gas in a container, and get a positive reading, the absolute pressure there is
actually the reading on the dial plus the pressure of the air column above. If
your tire measures 30psi at sea level, it will give a reading of 44.696 in space,
assuming both readings were taken at the same temperature.

The only thing that's absolute about the air in a tire is the number of gas
molecules that make it up. Assuming no leaks.

When the temperature increases, the gas molecules get angrier, and hit the
walls harder. Which affects higher pressure.

Having said that, I also want to stick a needle to the auto manufacturers.
"Cold temperature" what is it? Living in Canada that's 40 degrees on a
pleasant day. Living in Cairo it is 100 degrees on a pleasant day.

What is really relevant to tire pressure specs is;
1: What do you mr carmaker consider as operating temperature of the
tire
2: What pressure do you need this tire at operating temperature

I did state 'actual' not absolute.

So what I'm thinking is that the chart, by using 70°F as operating cold temperature, is suggesting is that if your tire indicates(via a tire gauge or dash TPMS) 32psi when it's only 30°F, the actual pressure is much lower. Hence the recommendation on the chart, at 30°, to inflate to an indicated 37psi in my case.

 

[emeron]

I did state 'actual' not absolute.

So what I'm thinking is that the chart, by using 70°F as operating cold temperature, is suggesting is that if your tire indicates(via a tire gauge or dash TPMS) 32psi when it's only 30°F, the actual pressure is much lower. Hence the recommendation on the chart, at 30°, to inflate to an indicated 37psi in my case.

There's the thing. Temperature is one of the 3 ingredients of an equation that yields pressure as its result. There's no actual or indicated pressure, change one thing in the equation, there will be a new pressure.

The chart suggest changing the number of gas molecules (pump air in tire) to change the pressure (increase) back to where it was before it dropped (due to a drop in temperature).

Another solution would be to shrink the tire.

 

[The_K_Man]

There's the thing. Temperature is one of the 3 ingredients of an equation that yields pressure as its result. There's no actual or indicated pressure, change one thing in the equation, there will be a new pressure.

The chart suggest changing the number of gas molecules (pump air in tire) to change the pressure (increase) back to where it was before it dropped (due to a drop in temperature).

Another solution would be to shrink the tire.

Clear as mud - thanks!

 

[emeron]

Clear as mud - thanks!

Yes, sorry about that. I do admit it isn't a good explanation, plumbing was never my strong suit.

Animals 400!

 

[03LXV6]

I can only guess that it is trying to say 32 psi at 0 degrees will expand to 39 at 70 degrees. If that's what it is trying to say then it is not clear at all.

I agree with this. Last January I drove from FL to NY. I normally keep my tires at around 33 cold and on a highway drive it usually gets up to 35/36. During my trip I stopped in Virginia over night and woke up to all 4 reading around 27. The temp was around 30 degrees. I filled back to 33 PSI before continuing my drive.

When I got back to FL my cold PSI was 36/37.I didn't keep the TPMS display up the entire drive back so I don't know how high they PSI got on the drive back once I hit the warmer states.

 

[qman]

In other words, a gauge reading of 39psi at 30°F is compensating for a gauge reading of 32psi at 70°.

Except that's backwards. Or I don't know what you mean by compensating.

 

[The_K_Man]

Except that's backwards. Or I don't know what
you mean by compensating.

This will explain it better than I could. The gauge does what the chart is suggesting. Link to instruction manual included:

Store

www.longacreracing.com

 

[jackpine]

I'm sorry, but I think you're all missing the point of the chart. I think increasing the cold tire pressure when the outside air temperature is low is to keep the "rolling" (driving) pressure at a certain level. If, in the summer you see a pressure of say, 38-40 PSI when driving and your cold tire pressure was 32, then in the winter, the tires will never get that hot when underway so you'd start at a higher cold inflation pressure to compensate.

The main danger to tires is excessive tire flex when driving, which weakens the cords. Low pressure also increases the likelihood of hydroplaning on wet roads, which may be more common in the winter.

- Jack

 

[emeron]

The point of this chart is to add air when it's cold outside so the additional air makes up for the drop in the temperature and the pressure while the car is being driven on the road stays the same.